1. Field of the Invention
The present invention relates to a capacitive angle detector for detecting a rotating angle of a rotating shaft.
2. Description of the Related Art
A conventional capacitive angle detector is disclosed in Japanese Patent Application Laid-Open No. HEI 4-83114. As shown in FIG. 34, this capacitive angle detector 100 includes a first stationary disk 101, a second stationary disk 102 and a rotating disk 103 arranged between the first and second stationary disks 101, 102. The first stationary disk 101 has on a lower surface thereof electrodes 101a, 101b which are offset from each other by 90.degree.. On the other hand, the second stationary disk 102 has on an upper surface thereof electrodes 102a, 102b which are arranged in the same manner as the electrodes 101a, 101b. Furthermore, the rotating disk 103 has on an upper surface thereof electrodes 103a, 103c, and it has on a lower surface thereof electrodes 103b, 103d. The electrodes 103a, 103b are located radially outward of the electrodes 103c, 103d.
The electrodes 101a, 103c and the electrodes 103d, 102a constitute a capacitor, while the electrodes 101b, 103a and the electrodes 103b, 102b constitute another capacitor. Capacitance values of these capacitors change in accordance with a rotating movement of the rotating disk 103 in the direction of A or in the other direction. That is, the capacitance of the capacitor constituted by the electrodes 101a, 103c and the electrodes 103d, 102a changes as indicated by 1a of FIG. 35, while the capacitance of the capacitor constituted by the electrodes 101b, 103a and the electrodes 103b, 102b changes as indicated by 1b of FIG. 35. These capacitance changes are phase-shifted from each other by 90.degree.. By detecting these capacitance changes, it is possible to detect a rotating angle in the whole range of 360.degree..
In this capacitive angle detector 100, however, the electrodes 103a, 103b and the electrodes 103c, 103d are disposed on radially different locations of the rotating disk 103. That is, the electrodes 103a, 103b are located radially outward of the electrodes 103c, 103d. Because the electrodes 103a, 103b and the electrodes 103c, 103d cause capacitive coupling, it is impossible to detect capacitance changes precisely. Hence, this capacitive angle detector 100 is unable to detect a rotating angle precisely.
It is an object of the present invention to provide a capacitive angle detector capable of detecting a rotating angle with a high precision.